全文获取类型
收费全文 | 68938篇 |
免费 | 5257篇 |
国内免费 | 2763篇 |
专业分类
电工技术 | 2174篇 |
技术理论 | 1篇 |
综合类 | 3605篇 |
化学工业 | 16982篇 |
金属工艺 | 3385篇 |
机械仪表 | 3119篇 |
建筑科学 | 1789篇 |
矿业工程 | 1541篇 |
能源动力 | 2316篇 |
轻工业 | 12895篇 |
水利工程 | 380篇 |
石油天然气 | 19675篇 |
武器工业 | 334篇 |
无线电 | 724篇 |
一般工业技术 | 3640篇 |
冶金工业 | 3549篇 |
原子能技术 | 131篇 |
自动化技术 | 718篇 |
出版年
2024年 | 214篇 |
2023年 | 915篇 |
2022年 | 1704篇 |
2021年 | 2120篇 |
2020年 | 2194篇 |
2019年 | 2129篇 |
2018年 | 1831篇 |
2017年 | 2291篇 |
2016年 | 2407篇 |
2015年 | 2259篇 |
2014年 | 3627篇 |
2013年 | 3977篇 |
2012年 | 4481篇 |
2011年 | 4706篇 |
2010年 | 3457篇 |
2009年 | 3226篇 |
2008年 | 2853篇 |
2007年 | 3920篇 |
2006年 | 4165篇 |
2005年 | 3713篇 |
2004年 | 3263篇 |
2003年 | 2983篇 |
2002年 | 2632篇 |
2001年 | 2202篇 |
2000年 | 1939篇 |
1999年 | 1586篇 |
1998年 | 1345篇 |
1997年 | 1101篇 |
1996年 | 863篇 |
1995年 | 688篇 |
1994年 | 579篇 |
1993年 | 382篇 |
1992年 | 325篇 |
1991年 | 216篇 |
1990年 | 157篇 |
1989年 | 116篇 |
1988年 | 61篇 |
1987年 | 54篇 |
1986年 | 27篇 |
1985年 | 65篇 |
1984年 | 56篇 |
1983年 | 40篇 |
1982年 | 31篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1951年 | 7篇 |
1944年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 540 毫秒
991.
介绍了180号废洗涤汽油的再生工艺,研究证明:优化后的再生工艺简单、操作方便,再生汽油完全满足航空产品零件清洗要求。 相似文献
992.
A monitoring program was performed to investigate heavy metal content alteration due to exploratory drilling for oil using non-aqueous fluids (NAFs) in Brazilian offshore, 900 m deep. Fourteen elements were monitored in 54 sites and it was verified that after drilling activities the average Ba concentration was remarkably increased with respect to background level, even 1 year after the activity. A minor increase in Mn and a moderate increase in Al concentrations were verified. The Cd, Cr, Ni, As, Co, Cu, Pb, V, and Zn concentrations were at the background levels, ca. 1 year after the NAFs drilling materials deposition on the seafloor. The Al, Ba, Cd, Cr, Cu, Ni and Zn mean concentrations were significantly different (P<0.05) between the three sampling operations (cruises) performed, while As, Cd, Fe and Pb presented different mean values according to the distance of the oil well, independent of the sampling operation. Interaction between sampling operation and distance was observed for Mn. In all sediment samples the Hg concentration was below the detection limit (0.07 μg g−1). 相似文献
993.
工艺条件对ZrO2粒度的影响 总被引:2,自引:0,他引:2
以工业ZrOCl2·8H2O和分析纯Nh3·H2O为主要原料,采用化学沉淀法制备了ZrO2纳米粒子,研究了不同阶段添加表面活性剂聚乙二醇(PEG)对ZrO2粉体颗粒尺寸的影响机理.通过测定ZrO2粉体比表面积计算出其粒度在10~40nm之间. 相似文献
994.
Effects of N application and water supply on yield, oil content and N accumulation by canola, cultivar Marnoo, grown on a heavy clay soil in the Goulburn Murray Irrigation Region were investigated. Treatments were rainfed (Rf) or watered at a deficit of 50 mm (40–60 mm, I50) beginning in the spring. N treatments were 0, 50, 100 or 200 kg N ha–1 at sowing or as split applications of 20/80, and 50/50 kg N ha–1 at sowing and rosette, respectively.Yield (Yg) ranged from 170 to 520 g m–2. Irrigation and N increased yield in both years. Grain yields were increased by N application on the irrigated treatments when 100 or 200 kg N ha–1 was applied. Oil concentrations ranged from a maximum of 46.4% in treatment N0 to a minimum of 40.6% in treatment N200 and was inversely related to seed N concentration. Although fertilizer N decreased oil concentration, it increased the yield of oil.Nitrogen accumulation (Nb) limited yield of all treatments and was described by the equation, Yg = 806[1-EXP(–0.039*Nb)]. This implied a decrease in yield per unit of Nb at the higher rates of fertilizer addition with consequent increases in grain N concentration.The efficiency of water use in the production of grain (WUEg) and biomass (WUEb) were 7.5 and 23 kg ha–1 mm–1 respectively. Nitrogen additions increased WUEg and WUEb in both seasons. Maximum values of 8.9 (WUEg 1986) and 26.8 (WUEb 1987) were measured from treatment N200. These data suggest that the crops made efficient use of the applied water. 相似文献
995.
石墨粉末化学镀镍及化学镀银工艺 总被引:1,自引:0,他引:1
石墨粉末经前处理、敏化和活化,采用碱性化学镀镍法镀一层镍,再化学镀连续性较好的银。讨论了化学镀镍和化学镀银各成分影响,经实验确定:镀镍石墨粉末进行两次化学镀银,可以得到外观为灰白色的银包镍粉。该粉密度小,测定其电阻率小于1.5×10-4Ω.cm,与硅橡胶制成橡胶胶料,在低频区电磁屏效能为82 dB,是一种高性能的导电导磁新型填料。 相似文献
996.
Maki Itoh Toshimitsu Suzuki Yoshihiko Tsujimoto Ken-ichi Yoshii Yoshinobu Takegami Yoshihisa Watanabe 《Fuel》1983,62(1):98-102
Thermal cracking of tar-sand bitumens has been carried out using a two-stage pyrolysis reactor with temperature zones of 440°C and 750–800°C, respectively. Feedstocks were pyrolysed in the first stage into cracked oils, which were carried to the second stage for subsequent pyrolysis. Only 12–14 wt% of ethylene was obtained from tar-sand bitumens at the residence time of 1.2 s in the second stage, although 27 and 16 wt% were obtained from Taching and Iranian heavy vacuum residues, respectively. The tar-sand bitumens contain shorter paraffinic straight-chains and have more branched molecules than the vacuum residues of petroleum. A straight-chain paraffin index is proposed, with which a good correlation was obtained between ethylene yield and the fraction of straight-chain paraffin carbons in the heavy oil. 相似文献
997.
998.
Aranzazu García M Victoria Ruiz-Méndez Concepción Romero Manuel Brenes 《Journal of the American Oil Chemists' Society》2006,83(2):159-164
By definition, virgin olive oil is consumed unrefined, although a great proportion of the olive oil produced has to be refined
to render it edible. Phenolic compounds are among the substances eliminated during the refining process; in the present work
these were characterized by HPLC, and their evolution during the different refining steps was studied. The complete refining
process removed most polyphenols from oils, but the behavior of individual compounds at each step also was observed. o-Diphenols
(hydroxytyrosol, catechol, and hydroxytyrosol acetate) and flavonoids (luteolin and apigenin) were eliminated first during
the alkaline treatment. Tyrosol and 4-ethylphenol remained in the oil until the deodorization step. A large amount of phenolic
compounds was discovered in the refining by-products such as soapstocks and deodorization distillates. In the latter streams,
the concentrations of tyrosol and 4-ethylphenol reached up to 149 and 3720 mg/kg by-product, respectively. This high level
of 4-ethylphenol and its well-known strong off-odor can interfere during further processing of the deodorization distillates,
and this must be taken into account when deciding what is to become of them. Similarly, the results of this work open the
possibility of recovering phenolic compounds from the “second centrifugation olive oils” by adding a new washing step prior
to the refining process. By including this new step, the most polar polyphenols, hydroxytyrosol and tyrosol, will diffuse
from oil to water and a concentration of up to 1400 mg/L of hydroxytyrosol may be achieved. 相似文献
999.
Ioannis Lambropoulos Ioannis G. Roussis 《European Journal of Lipid Science and Technology》2007,109(6):623-628
The antioxidant activity of Xinomavro red wine phenolic extracts in corn oil stripped of tocopherols was evaluated. One wine extract, at 100 mg/L total phenolics, rich in phenolic acids and flavonols, inhibited the oxidation of corn oil stripped of tocopherols to a greater extent than butylated hydroxyanisole, at 200 mg/L. Moreover, another extract, at 100 mg/L total phenolics, rich in flavanols, flavonols and tyrosol, also exhibited high inhibitory action. The present results indicate that some red wine phenolics – such as phenolic acids, flavonols or flavanols – may be strong antioxidants in corn oil. 相似文献
1000.
2006年国际原油价格变化趋势分析 总被引:1,自引:0,他引:1
近年来,国际石油价格一直保持高位运行状态。2006年国际石油市场的发展趋势将表现出需求强劲、OPEC影响力进一步减弱、各种不确定性政治和自然事件依然存在、基金积极参与以及美国主宰石油政治的特点,国际油价也因之将保持较高水平。以2002年年末至2006年年初的WTI原油价格数据为基础,构建ARIMA模型并对2006年度的油价走势进行分析和预测。预测结果显示,2006年WTI月平均油价运行区间为(60 ̄70)美元b/bl。 相似文献